Field of the Invention
The present invention relates to a method for manufacturing a fiber-reinforced plastic structure and a mold used for manufacturing a fiber-reinforced plastic structure.
Description of the Related Art
Being lightweight and excellent in mechanical strength, fiber-reinforced plastics (FRPs) are used for structural members of an aircraft and the like.
For example, a skin of an aircraft and a stringer reinforcing the skin are also formed of FRPs.
Here, as shown in Mitsubishi Heavy Industries Technical Review, Vol. 42, No. 5 (December 2005), “Research in the Application of the VaRTM Technique to the Fabrication of Primary Aircraft Composite Structures,” co-bond molding is performed in which a fiber base material as the FRP material of the stringer is disposed in a pre-molded skin, and a resin which is impregnated in the fiber base material is heated and cured. When the resin has cured to a predetermined hardness, the stringer is molded, and at the same time, the stringer is integrally bonded to the skin through an adhesive. Thus, a fiber-reinforced plastic structure is manufactured.
In the co-bond molding of the skin and the stringer, first, the skin is molded by using a mold. The molded skin is then removed from the mold and inspected with ultrasound. Thereafter, the skin is returned (reset) to the mold before the stringer is molded. Then, the stringer is molded while the FRP material of the stringer disposed on the skin is being pressed by a mandrel which is positioned relative to the mold.
In the above-described co-bond molding of the skin and the stringer, unless the skin is returned to the mold at the same position as where the skin was molded, the stringer ends up being molded at a position off a defined position. This makes it difficult to fit the stringer to its mating part.
In order that the skin can be reliably disposed at its original position in the mold, protrusions are formed at positions in the mold corresponding to two points in the skin which are apart from each other, and recessed parts are formed in the skin by printing the protrusions of the mold on the skin during molding of the skin. When returning the skin to the mold, fitting the protrusions of the mold respectively into the recessed parts of the skin allows the skin to be positioned relative to the mold.
However, accurate positioning by the printing approach as described above requires the mold to be made of Invar with a low thermal expansion coefficient, which drives up the material cost of the mold.
If the mold is made of a material with a high thermal expansion coefficient, the protrusions of the mold are printed on the skin while the mold is elongated due to the heat applied during molding, so that, once a normal temperature is reached, the pitch of the protrusions of the mold has become smaller than the pitch of the recessed parts of the skin. As a result, the skin cannot be reset in the state of being positioned relative to the mold.
The object of the present invention based on the above problem is to provide a method and mold for manufacturing a fiber-reinforced plastic structure which allow a demolded fiber-reinforced plastic member to be reset in the state of being positioned relative to the mold, while keeping the material cost of the mold low.